Heat treating furnace



3 Sheets-Sheet 1 Filed April 9. 1958 Oct. 3, 1961 J. D. BARNES 3,002,733

HEAT TREATING FURNACE Filed April 9, 1958 5 Sheets-Sheet z .a ,2, Jose hD. Barnes %WW BY F ATTOR EY Oct. 3, 1961 Filed April 9. 1958 J. D.BARNES HEAT TREATING FURNACE 5 Sheets-Sheet 3 3,002,733 HEAT TREATINGFURNACE Joseph D. Barnes, Meadville, Pa., assignor, by mesneassignments, to Sunbeam Equipment Corporation, a corporation of DelawareFiled Apr. 9, 1958, Ser. No. 727,312 4 Claims. (Cl. 263-3) The presentinvention relates to a heat treating furnace, and more particularlyrelates to a heat treating furnace for continuously moving strip.

The continuous handling and annealing of strip metal at greater andgreater production speeds has required the lengthening of the heatingpaths through which the continuously moving strip must pass for adequateand satisfactory heat treating. Lengthening of the heating paths has, ofcourse, increased the size of heat treating furnaces. The complexity ofcontaining and directing the heat to best advantage has become greaterwith the increased size of the furnaces. The heat treating ofcontinuously moving strip in large vertical heat treating furnaces hasgiven rise to another major problem, namely, control of the lateralmovement to and fro of long unsupported vertical lengths of strip as itpasses through the furnace. In furnaces of seventy to ninety feet tall,which are coming into use, the metal strip can easily rub the sides ofthe heating chamber with possible resultant damage both to the strip andthe heating chamber.

At the same time, the strip entering the' furnace at high productionspeeds, is sought to be brought up to furnace temperature as quickly aspossible sothat the strip, moving quickly through the furnace, will beat the desired soaking temperature for as long a period as is required.For this reason, the furnace is provided with a special heating sectionwhereinthe temperature of the strip is raised as quickly as possible tothe desired soaking temperature.

The object of my invention is to provide a continuously moving stripheat treating furnace with an initial heating passage capable ofstabilizing and centering the moving strip as it enters and travelsthrough the passage.

Another object of my invention is to provide a heat treating furnace forcontinuously moving strip with a means for rapid heat transfer to themoving strip entering the furnace.

Another object of my invention is to provide a heat treating furnacewhereby the continuous strip may enter with a minimum of heat loss fromthe furnace.

Other objects and advantages of my invention will be. readily apparentfrom the following detailed description, taken in conjunction with theaccompanying drawings, wherein:

FIGURE 1 is a vertical longitudinal sectional view of a verticalthree-pass strip furnace embodying the invention;

FIG. 2 is a side elevation view of part of the furnace as seen from theline II-II in FIG. 1; and

FIG. 3 is a sectional view substantially on the plane indicated by theline III-III in FIG. 2.

The general furnace construction is similar to that described andclaimed in the copending application of Willard Roth et al., Serial No.561,780, filed January 27, 1956, now United States Patent No. 2,926,902,granted March 1, 1960. The furnace has a tall heat insulated furnacehousing 2 which is supported on a base frame- Work 4, and which is freeto expand and contract verates Patent tically along suitable verticalguide bars 6. The housing 2 has an entry slit 8 which is located at thetop, and an exit slit 10 which is located at the bottom, althoughentrance and exit to the furnace may be had in any desired arrangement.The exit slit 10 is provided with suitable sealing means, such as aWater tank 11 presenting a barrier against gas leakage from the furnace.Heated gas is exhausted from the furnace in any suitable manner andredirected to heating means for return to the furnace through a plenumchamber 22. The housing 2 is otherwise as gas tight as it canconveniently be made.

Means are provided for directing the continuously moving strip 12through the furnace in one or more long,

substantially unsupported, vertical passes as the strip moves throughthe furnace. Rollers 14, suitably located at the top and bottom of thefurnace and driven by suitable means, move the strip through thefurnace. Pivoted arms 16 which are counterweighted at 13 provide meansfor swinging the rollers 14 in or out of the furnace for maintenance andreplacement purposes. Means for regulating strip tension either insideor external to the furnace may also be had in any suitable known manner.

The longitudinally moving strip 12 enters by means of the entry slit 8and, if desired, may have been preliminarily heated in a preheatingchamber, not shown, located above the furnace. Aport 20 leads to a pointoutside of the top of the furnace. The purpose of the port 20 is toprovide a means of indicating whether furnace gases are leaking out ofthe furnace through the entry slit 8, or whether air is being drawn inthrough the entry slit 8. Suitable apparatus, either in the form ofpressure sensitive dampers or temperature sensitive instruments, can beused to detect whether air is blowing in or furnace gases are escapingfrom the slit 8. These devices would serve as a criterion for adjustingexhaust valves, not shown, that expel the furnace products ofcombustion.

The heated gas introduced into the furnace by the plenum chamber 22flows through a heat exchange passage 24, the flow being generallyindicated by the arrows shown in the figure. Dampers 26 divide the flowof heated gas in any selected or desirable direction and quantity so asdistribute the heated gas to best advantage Within a long open-ended,tubular, heat insulated baffle 28 within the heat insulated furnacehousing 2, and the bottom space 30. By proper adjustment of the dampers26 it is possible to maintain the temperature within the baffle 28within very close limits as more fully explained in the aforementionedcopending application. If desired, additional space heaters may beinserted between the furnace housing 2 and the baffle 28 to make up anyheat loss through the furnace housing 2, and when such heaters are usedit may be possible to omit the dampers in some cases.

As mentioned previously, the long vertical unsupported length of stripentering the furnace through the heat exchange passage 24 is subject tothe possibility of fluttering or lateral movement which may damage thestrip or the heat exchange passage 24. At the same time, upon theinitial entry of the moving strip 12 into the furnace, it is desirableto increase the temperature of the strip to the soaking temperature ofthe furnace as quickly as possible so that the fast moving strip mayhave the benefit of proper soaking temperature for the greatest lengthof time.

In accordance with the present invention, the heat exchange passage 24is made of a plurality of hollow sections 34 whose walls, enclosing theflat sides of the strip, are divergent in the direction of the movingstrip and turn outward at the upper end thereof to provide a throat orconstriction 32 at the top of each section 34. In effect, the passage 24consists of convergent-divergent sections 34 secured endto-end inseries, and capable of creating sufficient turbulence of the heated gasover the moving strip 12 so as to increase the heat transfer from. theheated gas to the strip. More importantly, the spaced constrictionswithin the passage 24 (a constriction 32 for each section 34) providefor increased strip stability by directing the heated gas with equalpressure against each side of the strip 12. The static pressure build-upon either side of the moving strip 12 just downstream from the apex ofthe node formed by each constriction 32 will be equal on each side andwill tend to center the strip as it moves through the heat exchangepassage 24. In other words, the depressions or constrictions 32 furnishventuri sections with nodes creating a static pressure build-up justdownstream from the constrictions 32 so as to center the moving strip12. The portion of the section 34 beyond each constriction 32 flares outslowly so that the velocity of the gas can be reduced to minimize thefluid friction total pressure loss in the passage 24. Thus, the passage24 allows the maximum volume of heated gases to pass through into thefurnace with minimum loss while creating sufficient turbulenceforeffective heat transfer to the moving strip 12.

FIGS. 2 and 3 show an enlarged view of the plenum chamber 22 whichprovides means for admitting the heated gas into the heat exchangepassage 24 and hence into the heat insulated baffie 28 and the otherareas of the furnace. Twin inlet ducts 36, located on opposite sides ofthe heat exchange passage 24, allow entry of the heated gases into thechamber 22 from external heating and propelling means, not shown, whichmay be generally as described in the aforementioned copendingapplication. An exit passage 23 from the plenum chamber 22 is providedfor the gases to enter the heat exchange passage 24.

It is necessary that the plenum chamber 22 admit the heated gas into thefurnace in equal proportions on both sides of the longitudinally movingstrip 12. The twin inlet ducts 36 initially divide the heated gasesentering the plenum chamber 22. Two sets of crescent shaped vanes 38,each vane spaced equidistant from the adjacent vanes in its set, turnthe heated gas towards the upper space 40 of the plenum chamber 22. Thevanes 38 are diagonally disposed within the plenum chamber 22 in thedirection of gas flow, as shown in FIG. 2, and each set is located toreceive the heated gas entering from one of the twin inlet ducts 36.

As can be seen from the drawing, the heat exchange passage 24, by whichthe heated gases enter the furnace proper, has its beginning centrallylocated with respect to the walls of the plenum chamber 22 and justbelow a narrow entrance channel 25, which abuts the entry slit 8 andthrough which the strip enters the furnace and passes into the passage24. The heat exchange passage 24 has a mouth 42 extending laterally fromthe front wall to the back wall of the plenum chamber 22. The mouth 42is formed by streamlined lips 43 for a smooth well-rounded inlet at theentrance of the heat exchange passage 24. The lips 43 are shaped toafford entrance of the heated gases into the heat exchange passage 24with a minimum of fluid friction and are shaped to convert staticpressure energy into velocity pressure energy with a minimum energyloss. A low static pressure at this point makes it possible to have anopening into the furnace through which the moving strip 12 may enterwithout appreciable loss of the heated gases from the furnace.

Thus, it can be seen that the hot gases are initially divided and enterthe plenum chamber 22 Via the twin inlet ducts 36. The sets of turningvanes 38 evenly divide the heated gas to distribute it across the plenumchamber and direct it upward to the upper area 40. From the upper area40 the gas enters the mouth 42 of the heat exchange passage 24 wherehalf flows longitudinally along one face of the moving strip 12 whilethe other half of the heated gas flows longitudinally along the otherface of the moving strip. In this manner, equalized centering forceswill act upon the moving strip 12 during its travel through the heatexchange passage 24 at points just below each constriction 32 of eachsection 34, as previously described.

It is now readily apparent that a continuously moving strip heattreating furnace has been provided which has means for centering themoving strip in its travel through the heat exchange passage 24 whilebeing brought up to soaking temperature with a minimum of delay.Sufficient turbulence of the heated gases has been provided to insure anadequate transfer of heat from the gases to the moving strip, yet thefluid friction total pressure loss of the gas stream itself has beenminimized by the convergent-divergent sections 34 which provide venturisurfaces which not only minimize the pressure loss but also center thestrip. The plenum chamber 22 provides means for adequately controllingthe heated gases upon entry into the furnace so that little heat lossoccurs through the entry slit 8.

Whilethis invention has been described with a certain degree ofparticularity, it is to be understood that all modifications,alterations and combinations within the spirit and scope of my inventionare included.

I claim as my invention:

1. In a heat treating furnace, twin inlet ducts for the entrance ofheated gases, a plenum chamber including vertically extending side wallsand front and back walls for containing said gases, means defining aheat exchange passage equidistantly located from the side walls of theplenum chamber and having a mouth extending laterally between the frontand back walls, a plurality of substantially crescent shaped vanesfacing upward and disposed in two sets in the plenum chamber onoppositesides of said passage, each set diagonally disposed with each vanespaced equidistant from the adjacent vanes in its set, said passageextending into the main portion of the furnace, said passage definingmeans including a series of longitudinally aligned sections, eachsection having a constriction at the upper end thereof and slowlyflaring out therefrom towards the next section, and means for directinggases through said passage in equal proportion on each side of thestrip.

2. In a heat treating furnace, a tall insulated furnace housing, conduitmeans forming a thin heat exchange passage of substantial widthextending vertically within said housing, means for directing alongitudinally moving strip vertically through said passage, a plenumchamber positioned on both sides of the upper end of said passage andextending across the width thereof, horizontally extending openings atthe upper end of said passage providing fluid communication between saidplenum chamber and said passage, inlet ducts for introducing heatedgases into said plenum chamber, gas distribution means within saidplenum chamber for producing a constant gas flow across the entirelength of said horizontally extending openings;

3. A heat treating furnace comprising a furnace housing, walls definingan elongated heat exchange passageway within said housing, saidpassageway being narrow and of substantial width to closely enclose astrip of material moving longitudinally therethrough, means defining aplenum chamber at one end of said passageway extening across the widthof said passageway on both sides thereof, elongated openings extendingacross the width of said passageway and communicating between saidplenum chamber and said passageway, conduit means extending parallel tosaid elongated openings for supplying heated gases to said plenumchamber, vanes in said plenum chamher for delivering equal quantifies ofgas across the lengths of said openings.

4. A heat treating furnace comprising a furnace housing walls definingan elongated heat exchange passageway within said housing, saidpassageway being narrow and of substantial width to closely enclose astrip of material moving longitudinally therethrough, means defining aplenum chamber extending across the width of said passageway on bothsides thereof, elongated openings ex- 10 tending across the width ofsaid passageway, conduit means extending parallel to the width of saidpassageway for supplying heated gases to said plenum chamber, aplurality of crescent shaped vanes facing said conduit means and saidopenings and grouped in two sets, the

vanes of each set positioned along a line extending from a pointadjacent the end of each said opening closest to said conduit meansangularly away from said openings; and said conduits.

References Cited in the file of this patent UNITED STATES PATENTS1,847,915 Bailey Mar 1, 1932 2,434,169 Larsen Jan. 6, 1948 2,610,411Steese Sept. 16, 1952 2,775,046 Kabelitz Dec. 25, 1956 FOREIGN PATENTS819,028 France June 28, 1937 14,256 Great Britain 190 3

